These locomotive engines were long in use at Killingsworth Colliery, near Newcastle, and at Hetton Colliery, on the Wear; so that their advantages and defects have been sufficiently submitted to the test of experiment. " The principal objections (in the opinion of Mr. Galloway), consist in the difficulty of surmounting even the slightest ascent; for it has been found that a rise of only one-eighth of an inch in a yard,'or 18 feet in a mile, retards the speed of one of these engines in a very great degree; so much so, indeed, that it has been considered necessary, insome parts where they are used, to aid their ascent with their load by fixed engines, which drag them forward by means of ropes coiling round a drum. The steam cylinders below the boiler were found very defective, for in the ascending stroke of the working piston, they were forced inwards by the connecting-rod pulling at the wheel in turning it round, and in the descending stroke the same pistons were forced as much outwards: this motion or play rendered it necessary to increase the length of the working cylinder as much as there was play in the lower ones, to avoid the danger of breaking or seriously injuring the top and bottom of the former by the striking of the piston when it is forced too much up or down.
As our meaning may not be fully comprehended without elucidation, let us imagine the cylinder of a common beam engine to be set upon springs which have a play of one foot; the weight of the cylinder, when at rest, depresses the spring six inches; but if the engine be put in motion, then, as the piston ascends and gives motion to the machinery, the springs below the cylinder, being, as it were, the abutments upon which the steam acts, are forced downwards against their seat with precisely the force that the piston exerts in overcoming the resistance of the machinery. In like manner, when the piston descends, as much weight or pressure will be taken off these springs by the same means: the cylinder would, therefore, vibrate or dance upon the bearing springs; and as the motion which it thus obtains is the reverse of the motion then given to the piston, the length of the cylinder should be greater to allow for the extreme vibration to which it is liable. A quantity of steam would, therefore, be lost in filling up this extra length of the cylinder at each stroke.
This would also happen if the cylinder were fixed, as usual, and the carriages of the crank and fly-wheel supported upon springs; and this arrangement would then be exactly the same, in principle and effect, as the parts of the locomotive engine to which we now allude."
The engraving on the preceding page represents one of the engines made for the Kirkintilloch and Monkland Colliery Railway, by Messrs. Murdoch and Aitken of Glasgow. The working of these engines gave, it is said, very high satisfaction to the proprietors, as performing more work than the engineers undertook they should execute. As there appears to be nothing in the arrangement of the parts which was not previously known, we can only attribute the high character these engines attained, to superior workmanship - and the clothing of the engine in a wooden casing, to prevent the waste of heat. It affords a good example of the old fashioned locomotives, and shows a peculiar mode of coupling the wheels. The connecting rod between the two wheels has a ball and socket joint at each end, making universal joints. The wheels have a play of about one inch to allow for turning in the sharp curves of the line. The cylinders are 10 1/2 inches diameter each, and the stroke two feet, pressure of steam 50lbs. The average speed of these engines was 6 miles per hour, which is quite adequate for the purposes of a colliery.
They were the first locomotive engines made in Glasgow.
The improvements in the engine or carriage wheels proposed by Messrs. Stephenson and Losh, in their patent of 1816, consisted in forming the spokes of malleable iron, and uniting them in the sand by casting the ring and nave to them. In some cases, they made the "spokes of cast iron, with hoops, tires, or trods of malleable iron."
Fig. 1 is a side view of the wheels, with wrought-iron arms. a a a show the arms cast in the nave, and dropped into mortice holes made in the rim, which are dovetailed, to suit the dovetailed ends of the arms a a a. The arms are heated red hot previous to dropping them into the holes, in order to cause them to extend sufficiently for that purpose, for when cold they are too short, owing to the property which iron possesses, of expanding on the application of heat, and of contracting again to its former dimensions on cooling down to the same temperature from which it was raised; the arms, therefore, on cooling, are drawn with a force sufficient to produce a degree of combination between their dovetailed ends and the mortices of the rim, which prevents the possibility of their working loose; they are afterwards keyed up; the mortice holes are also dovetailed, from the tail side of the wheel (a a, Fig. 2.) to the crease side (b in the same figure).
Fig. 2 is a cross section through the centre of the wheel, with wrought-iron arms.
Fig. 3 is an end view of Fig. 2.
Fig. 4 represents an elevation of the edge railway, showing a rail a connected with the two adjoining rails, the ends of which are shown by b b, and resting in the props or pedestals, the bases of which are the metal chairs that are bolted to the stone supports c c. The joints e e are made by the ends of the rails being applied to each other by what is termed a half lap; and the pin or bolt g which fixes them to each other, and to the chair in which they are inserted, is made to fit exactly a hole which is drilled through the chair and both ends of the rails, at such a height as to allow both ends of the rails to bear on the chair, and the bearance being the apex of a curve, they both bear at the same point. Thus the end of one rail cannot rise above that of the adjoining one; for although the chair may move on the pin in the direction of the line of the road, yet the rails will still rest upon the curved surface of their bearance without moving.